Chlamylla Bergh, 1886

Korshunova, Tatiana, Martynov, Alexander, Bakken, Torkild, Evertsen, Jussi, Fletcher, Karin, Mudianta, I Wayan, Saito, Hiroshi, Lundin, Kennet, Michael Schroedl, & Picton, Bernard, 2017, Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda), ZooKeys 717, pp. 1-139 : 10-11

Chlamylla Bergh, 1886 Figs 2, 3, 4, 5, 6, 7

Type species.

Chlamylla borealis Bergh, 1886

Diagnosis.

Body wide. Notal edge present, well-defined, continuous. Cerata not stalked, continuous. Rhinophores smooth to wrinkled, longer than oral tentacles. Anterior foot corners absent. Anus pleuroproctic under the notal edge. Rachidian teeth with strong denticulated cusp; lateral denticles not clearly delineated from cusp. Lateral teeth weakly denticulated to smooth without attenuated process basally. Single distal receptaculum seminis. Wide granulated prostate. Thin, long vas deferens clearly separated from prostate. External permanent penial collar. Penis elongated conical, internal.

Species included.

Chlamylla borealis borealis Bergh, 1886, stat. n. (= Gonieolis atypica Bergh, 1899, syn. n.) (Fig. 3) (original description in Bergh 1886, 1899, 1900a), Ch. borealis orientalis (Volodchenko, 1941), comb. n. (Fig. 4) (original description in Volodchenko 1941), Chlamylla intermedia (Bergh, 1899), comb. n. (Figs 5, 6) (original description in Bergh 1899, 1900a).

Remarks.

Bergh (1886) described the genus Chlamylla based on the species Ch. borealis with a continuous notum, wide granulated prostate, and aberrant radula (lateral teeth with very broad bases, rachidian teeth completely lacking denticles and having instead a pair of unusual long processes ( Bergh 1886: Taf. 1, fig. 14). The true identity of the type species Ch. borealis with our extensive recent paracoryphellid specimens from the Arctic is a complicated question. Such radular features are completely unknown in the group of the Arctic Paracoryphellidae usually assigned to the genus Chlamylla ( Roginskaya 1987; Martynov 2006a) Figs 1, 3H, 4H, 5H, 6E). However, the general shape of the body, shape of the jaws, presence of a wide granulated prostate, and penial collar in Ch. borealis agree with specimens that are currently assigned to the species Ch. atypica and Ch. intermedia . Bergh in the same work (1886) described the radula of another species " Goniaeolis typica " in detail ( Bergh 1886: Taf. 3, fig. 14) as a normal triserial radula. However, Bergh (1886) also noted that the radula of Ch. borealis was in a poor condition. This may imply that either Bergh studied an abnormal specimen or had damaged the radula in some way during preparation. For this study we specially investigated the holotype of Ch. borealis (NHMD GAS-2055). It is dry and heavily dissected, but a separate cut-off of the external penial collar is left; the penis and damaged jaws are preserved. Comparison of available information from the holotype of Ch. borealis with figures from the original description ( Bergh 1886: Taf. 1, fig. 22) confirms the presence of an external penial collar with caudal genital fold. According to our data only two paracoryphellid species with a complex folded penial collar are known from Arctic seas and are currently identified as Chlamylla atypica and Ch. intermedia (Figs 3, 4C, 4I, 5J, 6F, 7). Morphologically these taxa differ from the rest of the traditional flabellinids, forming a distinct compact clade according to the present molecular analysis (Figs 1, 2), which demonstrates significant molecular divergence (more than 11%) from other members of the family Paracoryphellidae . Based on the details in the original description of Chlamylla and type material, we can conclude, under supposition that the radula was malformed or wrongly processed, that the type species Ch. borealis belongs to the same genus as known paracoryphellid species from the Arctic, currently identified as Ch. atypica and Ch. intermedia . Given that Ch. borealis was never found again, but inhabited the same region our other samples, it is highly likely that Ch. borealis is actu ally conspecific with one of the two currently known Chlamylla species. One of these species, Ch. intermedia (Bergh, 1899) possesses an external penial collar but without any traces of a caudal genital fold (Fig. 5J), whereas Ch. borealis , according to both its original description ( Bergh 1886: Taf. 1, fig. 22a) and our novel information from the holotype, possesses a short but evident caudal genital fold. Thus, we can conclude that Ch. intermedia cannot be a synonym of Ch. borealis . Another species, Ch. atypica which was described under the genus Goniaeolis from the Davis Strait, Greenland ( Bergh 1899, 1900a) readily differs from other Chlamylla species by the presence of a special long external genital fold towards the anal opening ( Bergh 1899, 1900a: Tab 4, fig. 6) (Fig. 3). Because Ch. borealis also possesses a genital fold, and given a high similarity of prostate patterns between our specimens previously identified as Ch. atypica (Fig. 3J) and the figure of the reproductive system with the characteristically bent prostate as in Ch. borealis in Bergh’s original description of Ch. borealis ( Bergh 1886, Taf. 1, fig. 21) we therefore conclude that Ch. atypica is most likely is a junior synonym of Ch. borealis . The differences between length of the genital fold of the holotype of Ch. atypica (also investigated in the present study, NHMD GAS-2090) and Ch. borealis is possibly due to considerable differences in the length of holotypes of Ch. borealis and Ch. atypica (the former is nearly two times shorter than the latter). Smaller specimens previously identified as Ch. atypica s. l. may possess a considerably shorter genital fold, especially in the preserved state (Fig. 4C). Therefore, in order to preserve current usage of the genus Chlamylla that has already appeared in a number of publications on Russian nudibranch fauna, we therefore synonymise here the species Ch. atypica with Ch. borealis .

The Japan Sea specimens are consistent with the Arctic specimens in the presence of the external genital fold, but due to minor differences in the radula and also a very large geographic gap we consider it as a subspecies Chlamylla borealis orientalis (Volodchenko, 1941), comb. n. (Fig. 4). Chlamylla borealis orientalis is locally abundant during winter in Northern Japan ( Hirano 1997, as Ch. atypica ) and in the Russian part of the Sea of Japan (Martynov, unpublished course work (1991) as Ch. atypica ; Martynov and Korshunova 2011; present study). Several specimens of other Chlamylla without such a fold from the Arctic seas (distributed at least from the Barents Sea to Laptev Sea) have no significant molecular differences between them (Figs 1, 2) and have consistent morphology (Figs 5-6) and clearly belong to the same species. The oldest name for this Chlamylla without a genital fold is Goniaeolis intermedia Bergh, 1899 also from the Davis Strait, Greenland. The lateral teeth of Goniaeolis intermedia with a broad base and slightly attenuated lateral processes ( Bergh 1899: tab 4, fig. 16) are similar to our material from the Arctic seas (Figs 5H, 6E). However, G. intermedia lacked denticles on the lateral teeth. The Arctic specimens show small, sometimes almost diminishing denticles (Fig. 6E). Such denticles are not always clearly evident. Possibly this species reaches at least the Bering Strait and potentially may enter the coldest shelf waters of the NW Pacific (i.e., Bering and Okhotsk Sea, Martynov 2006a). Coryphella barentsi Derjugin, 1924 ( Derjugin 1924a, b, preoccupied by Coryphella barentsi Vayssière, 1913 ( Vayssière 1913, see Gosliner and Griffiths 1981 suggesting a replacement name) is a possible synonym of Ch. intermedia (Bergh, 1899).